# Plottier Formation

The Plottier Formation is a geologic formation that outcrops in the Argentine Patagonian provinces of Río Negro and Neuquén. It is the younger of two formations belonging to the Río Neuquén Subgroup within the Neuquén Group of the Neuquén Basin, with the oldest rocks dating from the late Coniacian and its youngest maybe from the very start of the Santonian. Formerly, that subgroup was treated as a formation, and the Plottier Formation was known as the Plottier Member.

## Description

A section near the Neuquén City airport, north of the town of Plottier, is the type locality of the Plottier Formation. At its base, this formation grades into the Portezuelo Formation, and it is in turn overlain conformably by the Bajo de la Carpa Formation, a unit of the Río Colorado Subgroup.
The Plottier Formation is the thinnest formation within the Neuquén Group, with a maximum thickness of only 25 metres (82 ft). It is differentiated from the underlying Portezuelo Formation primarily by its higher content of argillites (mud deposits) and was deposited under fluvial conditions. In 2006, a detailed lithostratigraphic and paleoecological study of a section of the Plottier Formation was published. This section contained alluvial deposits laid down by what was essentially a low-gradient wandering river throughout the millions of years, but often was of a single-channel type with little meandering.

## Fossil content

| Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon | Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited. |
Few animal fossils are known from this formation, including:

### Crocodyliformes

Crocodyliformes reported from the Plottier Formation :
| Genus | Species | Presence | Material | Notes |
| Crocodyliformes indet. | Indeterminate | El Anfiteatro | Seven osteoderms (MPCA-AT 251–257) Right dentary fragment (MPCA-AT 75) | Resembles peirosaurids such as Peirosaurus and Uberabasuchus |
| Lomasuchus | L. palpebrosus | Embalse Cerros Colorados | Skull and partial mandibular ramus | A peirosaurid, specimen originally claimed to originate from the Rio Colorado formation. |
| Mesoeucrocodylia indet. | Indeterminate | Yacimiento Narambuena | Partial skeleton (MAU-PV-N-280) | Subadult specimen showing both derived and primitive traits |
| Peirosauridae indet. | Indeterminate | Puesto Hernández | Partial skeleton (MAU-Pv-PH-437) | A peirosaurid |

### Dinosaurs
#### Ornithischians

A footprint track of an ornithopod is known from the Middle Loma de la Lata site.
Ornithischians reported from the Plottier Formation :
| Genus | Species | Presence | Material | Notes | Images |
| Ornithopoda indet. | Indeterminate | El Anfiteatro | A pedal ungual phalanx (MPCA-AT 261) | An ornithopod roughly the size of Notohypsilophodon | |
| Ornithopoda indet. | Indeterminate | Puesto Hernández quarry | Partial dorsal neural arch (MAU-Pv-PH-458) | An ornithopod similar to Macrogryphosaurus, estimated to be 6 meters long | |

#### Sauropods

12 footprint tracks of a sauropod are known from the site of Proyecto Dino.
Sauropods reported from the Plottier Formation :
| Genus | Species | Presence | Material | Notes |
| Aeolosaurini indet. | Indeterminate | Yacimiento Narambuena | Four articulated caudal vertebrae (MAU-Pv-N-414) | A titanosaur |
| Antarctosaurus | A. giganteus | Aguada del Caño | Partial skeleton (MLP 26-316) | A titanosaur |
| Muyelensaurus | M. pecheni | Loma del Lindero | Partial skeleton & additional vertebrae | A titanosaur, specimens originally thought to be from the Portezuelo Formation |
| Notocolossus | N. gonzalezparejasi | Cerro Guillermo | Two partial skeletons (UNCUYO-LD 301 & UNCUYO-LD 302) | A titanosaur |
| Petrobrasaurus | P. puestohernandezi | Rincón de los Sauces | Partial skeleton | A titanosaur |
| Sauropoda indet. | Indeterminate | 5 kilometers north of Plottier | Partial right tibia (MCF-PVPH-899) | A sauropod |
| Sauropoda indet. | Indeterminate | Cerro Guillermo | Incomplete skeleton (IANIGLA-PV.113) | A sauropod |
| Titanosauria indet. | Indeterminate | El Anfiteatro | Incomplete dorsal vertebra (MPCA-AT 024) | A large titanosaur |
| Titanosauria indet. | Indeterminate | 5 kilometers north of Plottier | Left femur and partial ribs (MCF-PVPH-889) Right fibula (MCF-PVPH-900) | Remains of titanosaurs |

#### Theropods

Theropods reported from the Plottier Formation :
| Genus | Species | Presence | Material | Notes |
| Abelisauridae indet. | Indeterminate | Cañadon Amarillo | Tooth | An abelisaur tooth formerly thought to be part of the holotype specimen of Aerosteon |
| Abelisauridae indet. | Indeterminate | El Anfiteatro | Tooth (Endemas-PV 16) | An abelisaur, tooth originally reported as that of a carcharodontosaurid in 2009 but reclassified in 2021 |
| Alvarezsauria indet. | Indeterminate | Rincón de los Sauces | Right femur (MAU-Pv-PH-453) | An alvarezsaur |
| Brachyrostra indet. | Indeterminate | Loma del Lindero | Vertebrae, teeth and possible sacrum (MAU-Pv-LL-75) | An abelisaur |
| cf. Carcharodontosauridae | Indeterminate | El Anfiteatro | Tooth (Endemas-PV 16) | Reclassified as an abelisaur tooth in 2021 |
| Coelurosauria indet. | Indeterminate | El Anfiteatro | Two teeth (MPCA-AT 263 & 269) | A coelurosaur |
| Maniraptoriformes indet. cf. Unenlagiinae | Indeterminate | El Anfiteatro | Tooth (Endemas-PV 15) | Possible unenlagiine tooth, though more material is needed to confirm this |
| Theropoda indet. | Indeterminate | El Anfiteatro | Incomplete caudal vertebra (MPCA-AT 082) | A "moderately sized" theropod |

### Pterosaurs

Pterosaurs reported from the Plottier Formation :
| Genus | Species | Presence | Material | Notes | Images |
| Thanatosdrakon | T. amaru | Agua del Padrillo | Partial skeleton (UNCUYO-LD 307) Left humerus (UNCUYO-LD 350) | An azhdarchid | |

### Turtles

Turtles reported from the Plottier Formation :
| Genus | Species | Presence | Material | Notes |
| Chelidae? indet. | Indeterminate | El Anfiteatro | Plastron plate (MPCA-AT 089) | A chelid |
| Linderochelys | L. rinconensis | Loma de Lindero | Partial skeleton (MAU-PV-LL-69) | A chelid, locality originally assigned to the Rio Neuquén Subgroup with no specific formation. |
| Rionegrochelys | R. caldieroi | El Anfiteatro | Shell elements | A chelid, type specimen first reported as an indeterminate chelid in 2009 |

### Invertebrates

* Ichnofossils
** Scoyenia sp.
** Taenidium sp.
There are also ichnofossils left on the river's mudflats, as well as fossil freshwater bivalves.

#### Ostracods

Ostracods reported from the Plottier Formation :
| Genus | Species | Presence | Material | Notes |
| Cypridoidea indet. | Indeterminate | Zampal | A few specimens | A cypridoid |
| Ilyocypris | I. aff. bauruensis | Zampal | A few molts | An ilyocypridid |
| Ilyocypris | I. cf. riograndensis | Zampal | | An ilyocypridid |
| Ilyocypris | I. wichmanni | Zampal | | An ilyocypridid |
| Neocyprideis | N.? sp. | Zampal | | An ilyocypridid |
| Neocyprideis | N. zampalensis | Babilonia | 4 valves | An ilyocypridid |
| Neuquenocypris | N. calfucurensis | Babilonia | 3 valve fragments | An ilyocypridid |
| Neuquenocypris | N. cf. minor | Zampal | | An ilyocypridid |
| Neuquenocypris | N. nahuelniyuensis | Babilonia | 6 valves | An ilyocypridid |
| Neuquenocypris | N. tenuipunctata | Babilonia | 5 adult and 3 juvenile valves | An ilyocypridid |
| Paralimnocythere | P.? sp. | Zampal | Several carapaces and valves | A limnocytherid |
| Talicyprideinae sp. | Indeterminate | Zampal | Very scarce number of carapaces | An ilyocypridid |
| Vecticypris | V. sp. | Babilonia | 2 valves | A limnocytherid |
| Wolburgiopsis | W. cf. neocretacea | Zampal | | A limnocytherid |

### Plants

Plants reported from the Plottier Formation :
| Genus | Species | Presence | Material | Notes |
| Angiospermae? indet. | Indeterminate | Zampal | A few seeds | A possible angiosperm |
| Henrisporites | H. sp. | Zampal | Abundant megaspores | A lycopod |
| Lychnothamnus | L. barbosai | Zampal | Over 400 microfossils | A stonewort |
| Nitella | N. sp. | Zampal | 21 microfossils | A stonewort |
| Spermatites | S. sp. 1 | Zampal | Seeds | An angiosperm |
| Spermatites | S. sp. 2 | Zampal | Seeds | An angiosperm |